There are two possibilities... the Windows 8 issue or a registration issue. Here is the fix for the Windows 8 issue.

Windows 8 has a 'feature' that didn't occur in earlier operating system versions.

When you run as a Standard user and unlock TMG7 and TMG8, the program does not have the permission to write the registration information to the Registry, so the information is virtualized and written to the registry VirtualStore.

With WinVista and Win7, this worked fine.

Windows 8 comes along and periodically purges the registration information from the registry VirtualStore. That is why the program is locked again.

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The solution...

Step 1) You need to delete the registry key containing the virtualized information. This step is required for the solution to work.

Contact support (support@whollygenes.com) and see if they can walk you though it. In the meantime, you might try another possible fix. Rightclick on your TMG v8 icon on your desktop and select 'Run as Administrator.' Do this one time only.

That is good. I hope it is just not a temporary fix. Keep us posted. Again, you should run as Administrator this one time only, and note that 'running' as Administrator is different from 'logging in' as Administrator - which you should not do at all.